Strip casting apparatus with improved side dam force control

ABSTRACT

A method of casting a thin strip is disclosed. The method includes assembling a pair of side dams adjacent end portions of counter-rotating casting rolls through which a strip of metal can be cast to permit a casting pool of molten metal to be formed supported by the casting surfaces of the casting rolls, assembling an angular actuator connected to a side dam at an angle urging the side dam toward the casting pool with a hold down force component urging the side dam downwardly, assembling a metal delivery system above the casting rolls delivering molten metal to form a casting pool supported on the casting surfaces of the casting rolls above the nip and confined by the pair of side dams, and counter-rotating the casting rolls such that the casting surfaces of the casting rolls each travel inwardly to produce a cast strip downwardly from the nip.

BACKGROUND AND SUMMARY

This invention relates to making thin strip and more particularlycasting of thin strip by a twin roll caster.

It is known to cast metal strip by continuous casting in a twin rollcaster. Molten metal is introduced between a pair of counter-rotatinghorizontal casting rolls, which are cooled so that metal shells solidifyon the moving roll surfaces and are brought together at the nip betweenthe rolls to produce solidified strip product delivered downwardly fromthe nip between the rolls. The term “nip” is used herein to refer to thegeneral region at which the rolls are closest together. The molten metalmay be poured from a ladle into a smaller vessel, or tundish, from whichit flows through a transition piece to a metal delivery nozzlepositioned above the nip, longitudinally between the casting rolls,which delivers the molten metal to the region above the nip to form acasting pool of molten metal. The casting pool of molten metal issupported on the casting surfaces of the rolls above the nip. Thecasting pool is typically confined at the ends of the casting rolls byside plates or dams held in sliding engagement adjacent the ends of thecasting rolls.

In casting thin strip by twin roll casting, as the casting campaignproceeds the side dam are worn and move toward the center of the castingpool, causing a step down to form in the side dams. This can causeintermittent gaps to form between the side dams and the casting rollswhere skulls can form resulting in snake eggs in the cast thin strip.That in turn reduces the casting yield. There remains a need to improvecasting yield.

Disclosed is a method of casting thin strip comprising the steps of:assembling a pair of counter-rotating casting rolls laterally forming anip between circumferential casting surfaces of the rolls through whichmetal strip can be cast, assembling a pair of side dams adjacent endportions of the casting rolls to permit a casting pool of molten metalto be formed supported by the casting surfaces of the casting rolls,assembling an angular actuator connected to each side dam at an anglebetween 0.5° and 20° to the axis of the casting rolls to urging the sidedam toward the casting pool with a down force component urging the sidedam downwardly, assembling a metal delivery system above the castingrolls delivering molten metal to form a casting pool supported on thecasting surfaces of the casting rolls above the nip and confined by thepair of side dams, and counter-rotating the casting rolls such that thecasting surfaces of the casting rolls each travel inwardly toward thenip to produce a cast strip downwardly from the nip.

The angular actuator may be connected to each side dam through a swiveljoint. The angle of connection of the angular actuator to the side dammay be between 0.5° and 10° or between 0.5° and 5°.

Other details, objects and advantages of the invention will becomeapparent as the following description of embodiments of the inventionproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention in which:

FIG. 1 is a diagrammatical side view of twin roll caster systememploying the present twin roll caster;

FIG. 2 is a partial sectional view through the casting rolls mounted ina roll cassette in the casting position of the caster system of FIG. 1;

FIG. 3 is diagrammatical plan view of the roll cassette of FIG. 2removed from the caster;

FIG. 4 is a transverse partial sectional view through the portion marked4-4 in FIG. 3;

FIG. 5 is an enlarged view of one of the carriage assemblies marked asdetail 5 in FIG. 4;

FIG. 6 is a plan view, partially in section, of the actuator assemblyalong line 6-6 of FIG. 5 with illustrating the side dam in a firstposition; and

FIG. 7 is a side view in section of the side dam actuator assembly shownin FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to FIGS. 1 and 2, a twin roll caster system for continuouslycasting thin steel strip is comprised of a main machine frame 10 thatstands up from the factory floor and supports a roll cassette module 11with a pair of counter-rotatable casting rolls 12 mounted thereon. Thecasting rolls 12 have shaft portions 22 (FIG. 3) and casting surfaces12A laterally positioned to form a nip 18 there between. The castingrolls 12 are mounted on the roll cassette 11 for ease of operation andmovement of the casting rolls. The roll cassette facilitates rapidmovement of the casting rolls 12 ready for casting from a setup positioninto an operative casting position in the caster as a unit, and readyremoval of the casting rolls 12 from the casting position when thecasting rolls are to be replaced. There is no particular configurationof the roll cassette that is desired, so long as it performs thatfunction of facilitating movement and positioning of the casting rolls.

Molten metal is supplied from a ladle 13 through a metal deliverysystem, with a movable tundish 14 and a transition piece or distributor16. From the distributor 16, the molten metal flows to at least onemetal delivery nozzle 17, or core nozzle, positioned between the castingrolls 12 above the nip 18. Molten metal discharged from the deliverynozzle 17 is delivered to and forms casting pool 19 of molten metalabove the nip 18 supported on the casting surfaces 12A of the castingrolls 12. This casting pool 19 is confined in the casting area at theends of the casting rolls 12 by a pair of confining side closures orside dams 20 (shown in dotted line in FIG. 2). The upper surface of thecasting pool 19 (generally referred to as the “meniscus” level) may riseabove the bottom portion of the delivery nozzle 17 so that the lowerpart of the delivery nozzle 17 is immersed in the casting pool 19. Thecasting area includes the addition of a protective atmosphere above thecasting pool 19 to inhibit oxidation of the molten metal in the castingarea.

The ladle 13 typically is of a conventional construction supported on arotating turret 40. For metal delivery, the ladle 13 is positioned overa movable tundish 14 in the casting position to fill the tundish withmolten metal. The movable tundish 14 may be positioned on a tundish car66 capable of transferring the tundish from a heating station (notshown), where the tundish is heated to near a casting temperature, tothe casting position. A tundish guide, such as rails, may be positionedbeneath the tundish car 66 to enable moving the movable tundish 14 fromthe heating station to the casting position.

The movable tundish 14 may be fitted with a slide gate 25, actuable by aservo mechanism, to allow molten metal to flow from the tundish 14through the slide gate 25, and then through a refractory outlet shroud15 to a transition piece or distributor 16 in the casting position. Fromthe distributor 16, the molten metal flows to the delivery nozzle 17positioned between the casting rolls 12 above the nip 18.

The casting rolls 12 are internally water cooled so that as the castingrolls 12 are counter-rotated, shells solidify on the casting surfaces12A as the casting surfaces 12A move into contact with and through thecasting pool 19 with each revolution of the casting rolls 12. The shellsare brought together at the nip 18 between the casting rolls 12 toproduce a solidified thin cast strip product 21 delivered downwardlyfrom the nip 18. The gap between the casting rolls is such as tomaintain separation between the solidified shells at the nip so thatsemi-solid or “mushy” metal is present in the space between the shellsthrough the nip, and is, at least in part, subsequently solidifiedbetween the solidified shells within the cast strip below the nip.

FIG. 1 shows the twin roll caster producing the thin cast strip 21,which passes across a guide table 30 to a pinch roll stand 31,comprising pinch rolls 31A. Upon exiting the pinch roll stand 31, thethin cast strip may pass through a hot rolling mill 32, comprising apair of work rolls 32A, and backup rolls 32B, forming a gap capable ofhot rolling the cast strip delivered from the casting rolls, where thecast strip is hot rolled to reduce the strip to a desired thickness,improve the strip surface, and improve the strip flatness. The workrolls 32A have work surfaces relating to the desired strip profileacross the work rolls. The hot rolled cast strip then passes onto arun-out table 33, where it may be cooled by contact with a coolant, suchas water, supplied via water jets 90 or other suitable means, and byconvection and radiation. In any event, the hot rolled cast strip maythen pass through a second pinch roll stand 91 having rollers 91A toprovide tension of the cast strip, and then to a coiler 92. The caststrip typically may be between about 0.3 and 2.0 millimeters inthickness before hot rolling.

At the start of the casting campaign, a short length of imperfect stripis typically produced as casting conditions stabilize. After continuouscasting is established, the casting rolls are moved apart slightly andthen brought together again to cause this leading end of the cast stripto break away forming a clean head end of the following cast strip. Theimperfect material drops into a scrap receptacle 26, which is movable ona scrap receptacle guide. The scrap receptacle 26 is located in a scrapreceiving position beneath the caster and forms part of a sealedenclosure 27 as described below. The enclosure 27 is typically watercooled. At this time, a water-cooled apron 28 that normally hangsdownwardly from a pivot 29 to one side in the enclosure 27 is swung intoposition to guide the clean end of the cast strip 21 onto the guidetable 30 and feeds it to the pinch roll stand 31. The apron 28 is thenretracted back to its hanging position to allow the cast strip 21 tohang in a loop beneath the casting rolls in enclosure 27 before itpasses to the guide table 30 where it engages a succession of guiderollers.

An overflow container 38 may be provided beneath the movable tundish 14to receive molten material that may spill from the tundish. As shown inFIG. 1, the overflow container 38 may be movable on rails 39 or anotherguide such that the overflow container 38 may be placed beneath themovable tundish 14 as desired in casting locations. Additionally, anoverflow container (not shown) may be provided for the distributor 16adjacent the distributor 16.

The sealed enclosure 27 is formed by a number of separate wall sectionsthat fit together at various seal connections to form a continuousenclosure wall that permits control of the atmosphere within theenclosure. Additionally, the scrap receptacle 26 may be capable ofattaching with the enclosure 27 so that the enclosure is capable ofsupporting a protective atmosphere immediately beneath the casting rolls12 in the casting position. The enclosure 27 includes an opening in thelower portion of the enclosure, lower enclosure portion 44, providing anoutlet for scrap to pass from the enclosure 27 into the scrap receptacle26 in the scrap receiving position. The lower enclosure portion 44 mayextend downwardly as a part of the enclosure 27, the opening beingpositioned above the scrap receptacle 26 in the scrap receivingposition. As used in the specification and claims herein, “seal,”“sealed,” “sealing,” and “sealingly” in reference to the scrapreceptacle 26, enclosure 27, and related features may not be a completeseal so as to prevent leakage, but rather is usually less than a perfectseal as appropriate to allow control and support of the atmospherewithin the enclosure as desired with some tolerable leakage.

A rim portion 45 may surround the opening of the lower enclosure portion44 and may be movably positioned above the scrap receptacle, capable ofsealingly engaging and/or attaching to the scrap receptacle 26 in thescrap receiving position. The rim portion 45 may be movable between asealing position in which the rim portion engages the scrap receptacle,and a clearance position in which the rim portion 45 is disengaged fromthe scrap receptacle. Alternately, the caster or the scrap receptaclemay include a lifting mechanism to raise the scrap receptacle intosealing engagement with the rim portion 45 of the enclosure, and thenlower the scrap receptacle into the clearance position. When sealed, theenclosure 27 and scrap receptacle 26 are filled with a desired gas, suchas nitrogen, to reduce the amount of oxygen in the enclosure and providea protective atmosphere for the cast strip.

The enclosure 27 may include an upper collar portion supporting aprotective atmosphere immediately beneath the casting rolls in thecasting position. When the casting rolls 12 are in the casting position,the upper collar portion 27A is moved to the extended position closingthe space between a housing portion adjacent the casting rolls 12, asshown in FIG. 2, and the enclosure 27. The upper collar portion may beprovided within or adjacent the enclosure 27 and adjacent the castingrolls, and may be moved by a plurality of actuators (not shown) such asservo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, androtating actuators.

There is shown in FIG. 4 a pair of delivery nozzles 17 formed assubstantially identical segments made of a refractory material such aszirconia graphite, alumina graphite or any other suitable material. Itmust be understood that more than two delivery nozzles 17 may be used inany different sizes and shapes if desired. The delivery nozzles 17 neednot be substantially identical in size and shape, although generallysuch is desirable to facilitate fabrication and installation. Twodelivery nozzles 17 may be provided, each capable of movingindependently of the other above the casting rolls 12.

Each delivery nozzle 17 may be formed in one piece or multiple pieces.As shown, each nozzle 17 includes an end wall 23 positioned nearest aconfining side dam 20 as explained below. Each end wall 23 may beconfigured to achieve a particular desired molten metal flow in thetriple point region between the casting rolls 12 and the respective sidedam 20.

The side dams 20 may be made from a refractory material such as zirconiagraphite, graphite alumina, boron nitride, boron nitride-zirconia, orother suitable composites. The side dams 20 have a face surface capableof physical contact with the casting rolls and molten metal in thecasting pool.

A pair of carriage assemblies, generally indicated at 104, are providedto position the side dams 20 and the delivery nozzles 17. Asillustrated, the twin roll caster is generally symmetrical, althoughsuch is not required. Referring to FIGS. 5-7, one carriage assembly 104is illustrated and described below, with the other carriage assembly 104being generally similar. It is understood that the twin roll caster mayutilize any number of carriage assemblies 104 configured in any suitablemanner to provide a flow of molten metal to the casting pool 19. Eachcarriage assembly 104 is disposed at one end of the pair of castingrolls 12. Each carriage assembly 104 may be mounted fixed relative tothe machine frame 10, or may be moveable toward and away from thecasting rolls 12 to enable the spacing between the carriage assembly 104and the casting rolls 12 to be adjusted. The carriage assemblies 104 maybe preset in final position before a casting campaign to suit the widthof the casting rolls 12 for the strip to be cast, or the position of thecarriage assembly 104 may be adjusted as desired during a castingcampaign. The carriages 104 may be positioned one at each end of theroll assembly and moveable toward and away from one another to enablethe spacing between them to be adjusted. The carriages can be presetbefore a casting operation according to the width of the casting rollsand to allow quick roll changes for differing strip widths. Thecarriages 104 may be positioned so as to extend above the casting rollswith the nozzles 17 positioned beneath the distributor 16 in the castingposition and at a central position to receive the molten metal.

For example, the carriage assembly 104 may be positioned from tracks(not shown) on the machine frame 10, which may be mounted by clamps orany other suitable mechanism. Alternatively, the carriage assembly 104may be supported by its own support structure relative to the castingrolls 12.

The carriage assembly 104 includes a support frame 125. A nozzle bridge108 is moveably connected to the support frame 125 and engages thedelivery nozzles 17 for selective movement thereof. A nozzle actuator110 is mounted to the support frame 125 and connected to the nozzlebridge 108 for moving the nozzle bridge 108 and in turn moving thedelivery nozzles 17 to position the end wall 23 relative to the side dam20. The nozzle actuator 110 is thus capable of positioning the deliverynozzles 17. The nozzle actuator 110 is a conventional servo mechanism.It must be understood, however, that the nozzle actuator 110 may be anydrive mechanism suitable to move and adjust delivery nozzles 17. Forexample, the nozzle actuator 110 may be a screw jack drive operated byan electric motor, a hydraulic mechanism, a pneumatic mechanism, a gearmechanisms, a cog, a drive chain mechanism, a pulley and cablemechanism, a drive screw mechanism, a jack actuator, a rack and pinionmechanism, an electro-mechanical actuator, an electric motor, a linearactuator, a rotating actuator, or any other suitable device.

As shown in FIGS. 2-3, cleaning brushes 36 are disposed adjacent thepair of casting rolls 12, such that the periphery of the cleaningbrushes 36 may be brought into contact with the casting surfaces 12A ofthe casting rolls 12 to clean oxides from the casting surfaces duringcasting. The cleaning brushes 36 are positioned at opposite sides of thecasting area adjacent the casting rolls 12, between the nip 18 and thecasting area where the casting rolls enter the protective atmosphere incontact with the molten metal casting pool 19.

The side dams 20 may be mounted on and actuated by plate holders 100positioned one at each end of the roll assembly and moveable toward andaway from one another. The plate holders 100 and side dams 20 may bepositioned on a core nozzle plate 106 mounted on the roll cassette 11 soas to extend horizontally above the casting rolls, as shown in FIG. 3.The core nozzle plate 106 is positioned beneath the distributor 16 inthe casting position and has a central opening 107 to receive the metaldelivery nozzle 17. The metal delivery nozzle 17 may be provided in twoor more segments, and at least a portion of each metal delivery nozzle17 segment may be supported by the core nozzle plate 106. The outer endof each metal delivery nozzle 17 is supported by a bridge portion (notshown) positioned adjacent the side dams 20 and capable of supportingand moving the delivery nozzle 17 during casting.

A nozzle position sensor 113 senses the position of the delivery nozzles17. The nozzle position sensor 113 is a linear displacement sensor tomeasure the change in position of the nozzle bridge 108 relative to thesupport frame 125. The nozzle position sensor 113 may be any sensorsuitable to indicate any parameter representative of a position of thedelivery nozzles 17. For example, the nozzle position sensor 113 may bea linear variable displacement transformer to respond to the extensionof the nozzle actuator 110 to provide signals indicative of movement ofthe delivery nozzles 17, or an optical imaging device for tracking theposition of the delivery nozzles 17 or any other suitable device fordetermining the location of the delivery nozzles 17.

The side dam 20 is mounted to a plate holder 100 which is moveablyconnected to the support frame 125 and engages the side dam 20 forselective movement thereof. A side dam actuator 102 is mounted to thesupport frame 125 and connected to the plate holder 100 for moving theplate holder 100 and thus moving each side dam 20 to position the sidedam 20 relative to the casting rolls 12. The side dam actuator 102 isthus capable of positioning the side dam 20, and may be capable ofcyclically varying the axial force of the side dams as described below.The side dam actuator 102 is a hydraulic force cylinder. It must beunderstood, however, that the side dam actuator 102 may be any suitabledrive mechanism to position the plate holder 100 to bring the side dam20 into engagement with the casting rolls 12 to confine the casting pool19 formed on the casting surfaces 12A during a casting operation. Such asuitable drive mechanism, for example, may be a servo mechanism, a screwjack drive operated by electric motor, a pneumatic mechanism, a gearmechanisms, a cog, a drive chain mechanism, a pulley and cablemechanism, a drive screw mechanism, a jack actuator, a rack and pinionmechanism, an electro-mechanical actuator, an electric motor, a linearactuator, a rotating actuator, or any other suitable device. Thus, theside dams 20 are mounted in side dam plate holders 100, which aremovable by side dam actuators 102, such as a servo mechanism, to bringthe side dams 20 into engagement with the ends of the casting rolls.Additionally, the side dam actuators 102 are capable of positioning theside dams 20 during casting. The side dams 20 thus form end closures forthe molten pool of metal on the casting rolls during the castingoperation.

A side dam position sensor 112 senses the position of the side dam 20.The side dam position sensor 112 is a linear displacement sensor tomeasure the actual change in position of the plate holder 100 relativeto the support frame 125. The side dam position sensor 112 may be anysensor suitable to indicate any parameter representative of a positionof the side dam 20. For example, the side dam position sensor 112 may bea linear variable displacement transducer to respond to the extension ofthe side dam actuator 102 to provide signals indicative of position ofthe side dam 20, or an optical imaging device for tracking the positionof the side dam 20 or any other suitable device for determining thelocation of the side dam 20. The side dam position sensor 112 may alsoor alternatively include a force sensor, or load cell for determiningthe force urging the side dam 20 against the casting rolls 12 andproviding electrical signals indicative of the force urging the side damagainst the casting rolls.

Illustrated in FIGS. 6 and 7, the side dam actuator 102 includes acylinder 124 and shaft 126 for converting pressure into a linear force.The shaft 126 is connected to a water cooling assembly 128 that providescooling to the side dam assembly. The water cooling assembly 128 isjoined to the plate holder 100 by a swivel joint 130. As discussedabove, the side dam 20 is mounted to the plate holder 100 of the sidedam system. Indicated in FIG. 7, each side dam actuator 102 is providedat an angle relative to the casting rolls 12 so that each side damactuator provides with a downward force component to the side dams 20relative to casting rolls 12 and inwards towards the casting pool 19.

During a casting campaign, the end portions of casting rolls 12 rubagainst the side dams 20 and cause a step-down to form in the side dams20. In the past, this step-down in turn has caused a gap to formintermittently between the side dam 20 and casting roll 12 into whichmolten metal from the casting pool 19 may be deposited, resulting inskull formation in the gap that can result in snake eggs being formed inthe cast product. However, in the present system, the side dam actuator102 providing an angular force to the side dams 20 with a downwardcomponent relative to the casting rolls 12, the side dams 20 will beshifted downward relative to the casting rolls 12 preventing a gap andin turn skulls from forming between a side dams 20 and a casting roll12, and preventing snake egg formation in the thin metal strip.

A component of the angular hold down side dam actuator 102 may be thepresence of a swivel joint 130 that transmits force from the side damactuator 102 to the plate holder 100. This allows the side dam 20 to beurged towards the casting pool 19 and towards the casting rolls 12without twisting or bending.

According to the illustrated embodiment, the angular hold down side damactuator 102 is provided at a 6° angle. However, the angular hold downside dam actuator may be provided at between 0.5° and 20°, depending onavailable space and optimal working conditions. More specifically, thehold down side dam actuator may be provided at an angle between 0.5° and10° or between 0.5° and 5°.

While the principle and mode of operation of this invention have beenexplained and illustrated with regard to particular embodiments, it mustbe understood, however, that this invention may be practiced otherwisethan as specifically explained and illustrated without departing fromits spirit or scope.

What is claimed is:
 1. A method of casting thin strip comprising thesteps of: assembling a pair of counter-rotating casting rolls laterallyforming a nip between circumferential casting surfaces of the rollsthrough which metal strip can be cast, assembling a pair of side damsadjacent end portions of the casting roll to permit a casting pool ofmolten metal to be formed supported by the casting surfaces of thecasting rolls, assembling an angular actuator connected to a side dam atan angle between 0.5° and 20° to the axis of the casting rolls to urgingthe side dam toward the casting pool with a hold down force componenturging the side dam downwardly assembling a metal delivery system abovethe casting rolls delivering molten metal to form a casting poolsupported on the casting surfaces of the casting rolls above the nip andconfined by the pair of side dams, and counter-rotating the castingrolls such that the casting surfaces of the casting rolls each travelinwardly toward the nip to produce a cast strip downwardly from the nip.2. The method of casting thin strip as claimed in claim 1 where theangle of connection of the angular actuator to each side dam is between0.5° and 10°.
 3. The method of casting thin strip as claimed in claim 1where the angle of connection of the angular actuator to each side damis between 0.5° and 5°.
 4. The method of casting thin strip as claimedin claim 1 where the angular actuator connected to each side dam througha swivel joint.